provides a tremendous opportunity to monitor weather in space," said Brian Anderson, of the Johns Hopkins Applied Physics Laboratory, Laurel, Maryland. Anderson and his colleagues presented their research on Friday during the fall meeting of the American Geophysical Union here.
Each of the roughly 70 satellites that make up the heart of the Iridium constellation comes equipped with a magnetometer, which measures Earth’s magnetic field.
While many satellites come similarly outfitted, what’s unique to Iridium is the coverage the swarm of polar-orbiting satellites provides, as the birds spin about Earth at an altitude of 484 miles (780 kilometers). It’s like having 70 distinct space-weather stations splayed across the globe.
The benefit of such a far-flung network is clear. Unlike, say, an Alaskan cold front, it’s no mean feat keeping tabs on space weather. As the solar wind buffets the Earth’s field, it can create an enormous cavity as large as 160,000 miles (256,000 kilometers) across, only to rapidly shrink again.
"It can change volume perhaps by 10 times in the space of an hour," Anderson said.
As each satellite passes through the electric current between space and Earth’s own atmosphere, its magnetometer can detect the distinct signatures of that current. Multiply that data by the number of Iridium satellites, and the distributed constellation gives scientists continuous measurements of the magnetic fields above Earth’s poles.
Scientists have coupled that data with radar measurements of the electric field over the same regions where Iridium measures magnetic fields.
"Putting those together, you can get the global electrical power coming in," said Colin Waters, of the University of Newcastle, New South Wales, Australia.
That allows scientists to monitor – on a continuous basis – electric currents between space and Earth’s upper atmosphere. The data also contribute to the first maps to show the flow of electric power into the upper atmosphere above the poles.
Experts are keen on keeping a close eye on space weather, since it can disrupt everything from power grids to communications. Shifts in the solar wind can also create "hotspots" where energy flows into the upper atmosphere, puffing it out to increase drag on orbiting satellites.
"With space weather, as we advance technologically, we are actually putting ourselves at greater risk," said Robert Robinson, director of the National Science Foundation’s magnetosphere physics program, which sponsors the work.
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